1. Field of the Invention
The present invention relates to a semiconductor device, particularly relates to a semiconductor device using ACF (anisotropic conductive film), a method for making the same, and an LCD monitor comprising the semiconductor device.
2. Description of the Related Arts
In some electric devices, components are connected with anisotropic conductive film, hereinafter referred to as ACF. ACF is comprised of a nonconductive synthetic resin and a plurality of conductive particles mixed therein.
FIG. 1A shows the sectional view of a conductive particle 1. Typically, a conductive particle 1, having a diameter of substantially 3 to 5 μm, is comprised of a central portion 1a made by some polymers. The outer surface thereof is further coated with a layer of conductive material 1b, such as Au, Ni, Zn, and so on.
ACFs are usually applied in the manufacture of LCD monitors. Sometimes, an ACF is used in connecting the driving chips to the glass substrate of the LCD. Manufacturers refer to this process as COG, i.e., chip on glass. In other cases, an ACF may be applied in connecting the driving chip to a flexible printed circuit (hereinafter referred to as FPC) located on the substrate. This process is referred to as COF.
Additionally, an ACF is also adapted to connect the chip onto a typical printed circuit board, and the process is referred to as COB.
FIG. 1B shows an application of the ACE. In this case, a substrate 4 is formed with some pads 4a, which are provided for transferring plural signals or energy. On the other side, there is a chip 3 comprised of plural electrodes, wherein the electrodes are respectively formed with a bump 3a. The ACF 5 is provided to connect the chip 3 and the substrate 4.
Firstly, the ACF is placed between the two devices, as shown in FIG. 1B. The ACF is heated, reducing the viscosity of the synthetic resin therein. Then, the chip 3 is compressed toward the substrate 4 with the bumps 3a aligned to the corresponding pads 4a. 
As shown FIG. 1B, some conductive particles 1 in the ACFs are clipped between the bumps 3a and pads 4a, thereby bumps 3a and the pads 4a are electrically connected by the metal layers 1b on the bumps 3a. 
In using the ACF, some common problems may occur. The conductive particles may be improperly shifted as the heated ACF is compressed between the components connected. One problem is shown in FIG. 1C. In the figure, the number of conductive particles 1 clipped by the bumps 3a and the pads 4a is insufficient, and the impedance between the terminals will increase. Another typical problem is shown in FIG. 1D, wherein the conductive particles 1 between two adjacent bumps 3a are highly concentrated, and a short circuit may occur. As microtechnology develops, there is a corresponding increase in the tendency to produce more concentrated chip bumps, with a commensurate increase in the potential for short-circuiting. Addressing the problems, U.S. Pat. No. 5,844,314 provides a structure shown in FIG. 1E. Two ends of the bump 3a are formed with projections 3a1, trapping the conductive particles 1 between the bump 3a and the pad 4a, and maintaining the conductivity of the connecting segment. Additionally, as shown in FIG. 1F, U.S. Pat. No. 5,903,056 provides a method of forming protrusions on the substrate 4 on both sides of the pads 4a, thereby approaching a similar effect to U.S. Pat. No. 5,844,314.
However, U.S. Pat. No. 5,844,314 and U.S. Pat. No. 5,903,056 have not yet solved the problem of short circuits.
As shown in FIG. 1G, U.S. Pat. No. 5,650,919 provides a method to prevent short-circuiting. On the substrate 4, peak-shape dielectric dams 6 are formed between adjacent pads. Thereby, the conductive particles 1 are constrained in predetermined spaces, and short-circuiting can be simultaneously prevented.
However, as shown in FIG. 1H, U.S. Pat. No. 5,650,919 cannot prevent the conductive particles 1 from shifting along the routes indicated by the arrows. In this case, high impedance and short-circuiting are still potential problems. Furthermore, the base 6a of a peak-shape dielectric dam 6 occupies a large space, and may block the bumps in a connection. Therefore, the connection must be aligned rather precisely, and insidiously the manufacturing cost will increase.
Additionally, in the connection, if a misalignment occurs, or a mounted chip is defective, a reworking process is then required to remove the chip from the substrate. The rework may damage the barrier structures, such as the dielectric dam. For the prior arts always form barrier structures on the substrate, if any barrier structure is damaged, the effect of constraining conductive particles 1 will decrease, unless a new set of barrier structures is formed on the substrate. Therefore, a variation for the substrate-based barrier structures in the prior arts is also preferable.